Identification of gag and env gene products of human T-cell leukemia virus (HTLV)

Cancer immunotherapy: it's time to better predict patients' response

In less than a decade, half a dozen immune checkpoint inhibitors have been approved and are currently revolutionising the treatment of many cancer (sub)types. With the clinical evaluation of novel delivery approaches (e.g. oncolytic viruses, cancer vaccines, natural killer cell-mediated cytotoxicity) and combination therapies (e.g. chemo/radio-immunotherapy) as well as the emergence of novel promising targets (e.g. TIGIT, LAG-3, TIM-3), the 'immunotherapy tsunami' is not about to end anytime soon. However, this enthusiasm in the field is somewhat tempered by both the relatively low percentage (<15%) of patients who display an effective anti-cancer immune response and the inability to accurately identify them. Recently, several existing or acquired features/parameters have been shown to impact the efficacy of immune checkpoint inhibitors. In the present review, we critically discuss current knowledge regarding predictive biomarkers for checkpoint inhibitor-based immunotherapy, highlight the missing/unclear links and emphasise the importance of characterising each neoplasm and its microenvironment in order to better guide the course of treatment.

The N93D mutation of the human T-cell leukemia virus type 1 envelope glycoprotein found in symptomatic patients enhances neuropilin-1 b1 domain binding

Human T-cell leukemia virus type 1 (HTLV-1) infection of host cells is mainly mediated by interactions with the viral envelope glycoprotein surface unit (SU) and three host receptors: heparan sulfate proteoglycan, neuropilin-1 (Nrp1), and glucose transporter type 1. Residues 90-94 of SU are considered as a Nrp1 binding site, and our previous results show that an SU peptide consisting of residues 85-94 can bind directly to the Nrp1 b1 domain with a binding affinity of 7.4 μM. Therefore, the SU peptide is expected to be a good model to investigate the SU-Nrp1 interaction. Recently, the N93D mutation in the Nrp1 b1 binding region of the SU was identified in symptomatic patients with HTLV-1 infections in the Brazilian Amazon. However, it remains unclear how the SU-N93D mutation affects Nrp1 b1 binding. To elucidate the impact of the substituted Asp93 of SU on Nrp1 b1 binding, we analyzed the interaction between the SU-N93D peptide and Nrp1 b1 using isothermal titration calorimetry and nuclear magnetic resonance. The SU-N93D peptide binds directly to Nrp1 b1 with a binding affinity of 3.5 μM, which is approximately two-fold stronger than wild-type. This stronger binding is likely a result of the interaction between the substituted residue Asp93 of the N93D peptide and the four residues Trp301, Lys347, Glu348, and Thr349 of Nrp1 b1. Our results suggest that the interaction of SU Asp93 with the four residues of Nrp1 b1 renders the high affinity of the N93D mutant for Nrp1 b1 binding during HTLV-1 entry.

HTLV-1 oncovirus-host interactions: From entry to the manifestation of associated diseases

Human T lymphotropic virus type-1 (HTLV-1) is a well-known human oncovirus, associated with two life-threatening diseases, adult T cell leukaemia/lymphoma (ATL) and HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP). The study of this oncogenic virus is significant from two different aspects. First, HTLV-1 can be considered as a neglected public health problem, which may spread slowly worldwide. Second, the incidence of HTLV-1 associated diseases due to oncogenic effects and deterioration of the immune system towards autoimmune diseases are not fully understood. Furthermore, knowledge about viral routes of transmission is important for considering potential interventions, treatments or vaccines in endemic regions. In this review, novel characteristics of HTLV-1, such as the unusual infectivity of virions through the virological synapse, are discussed in the context of the HTLV-1 associated diseases (ATL and HAM/TSP).

A novel neuropilin-1-binding sequence in the human T-cell lymphotropic virus type 1 envelope glycoprotein

Entry of human T-cell lymphotropic virus type 1 (HTLV-1) into host cells is mainly mediated by interactions between the viral envelope glycoprotein surface unit (SU) and three host receptors: glucose transporter type 1, heparin/heparan sulfate proteoglycan, and neuropilin-1 (Nrp1). Here, we analyzed the interaction between HTLV-1 SU and Nrp1 using nuclear magnetic resonance and isothermal titration calorimetry. We found that two SU peptides, residues 85-94 and residues 304-312, bound directly to the Nrp1 b1 domain with affinities of 7.4 and 17.7 μM, respectively. The binding modes of both peptides were almost identical to those observed for Tuftsin and vascular endothelial growth factor A binding to the Nrp1 b1 domain. These results suggest that the C-terminal region of HTLV-1 SU contains a novel site for direct binding of virus to the Nrp1 b1 domain. Our biophysical characterization of the SU peptides may help in developing inhibitors of HTLV-1 entry.

Human T lymphotropic virus type 1 SU residue 195 plays a role in determining the preferential CD4+ T cell immortalization/transformation tropism

Human T lymphotropic virus type 1 (HTLV-1) mainly causes adult T cell leukemia and predominantly immortalizes/transforms CD4(+) T cells in culture. HTLV-2 is aleukemic and predominantly immortalizes/transforms CD8(+) T cells in culture. We have shown previously that the viral envelope is the genetic determinant of the differential T cell tropism in culture. The surface component (SU) of the HTLV-1 envelope is responsible for binding to the cellular receptors for entry. Here, we dissect the HTLV-1 SU further to identify key domains that are involved in determining the immortalization tropism. We generated HTLV-1 envelope recombinant virus containing the HTLV-2 SU domain. HTLV-1/SU2 was capable of infecting and immortalizing freshly isolated peripheral blood mononuclear cells in culture. HTLV-1/SU2 shifted the CD4(+) T cell immortalization tropism of wild-type HTLV-1 (wtHTLV-1) to a CD8(+) T cell preference. Furthermore, a single amino acid substitution, N195D, in HTLV-1 SU (Ach.195) resulted in a shift to a CD8(+) T cell immortalization tropism preference. Longitudinal phenotyping analyses of the in vitro transformation process revealed that CD4(+) T cells emerged as the predominant population by week 5 in wtHTLV-1 cultures, while CD8(+) T cells emerged as the predominant population by weeks 4 and 7 in wtHTLV-2 and Ach.195 cultures, respectively. Our results indicate that SU domain independently influences the preferential T cell immortalization tropism irrespective of the envelope counterpart transmembrane (TM) domain. We further showed that asparagine at position 195 in HTLV-1 SU is involved in determining this CD4(+) T cell immortalization tropism. The slower emergence of the CD8(+) T cell predominance in Ach.195-infected cultures suggests that other residues/domains contribute to this tropism preference.

New insight into the oncogenic mechanism of the retroviral oncoprotein Tax

Human T cell leukemia virus type 1 (HTLV-1), an etiological factor that causes adult T cell leukemia and lymphoma (ATL), infects over 20 million people worldwide. About 1 million of HTLV-1-infected patients develop ATL, a highly aggressive non-Hodgkin's lymphoma without an effective therapy. The pX region of the HTLV-1 viral genome encodes an oncogenic protein, Tax, which plays a central role in transforming CD4+ T lymphocytes by deregulating oncogenic signaling pathways and promoting cell cycle progression. Expression of Tax following viral entry is critical for promoting survival and proliferation of human T cells and is required for initiation of oncogenesis. Tax exhibits diverse functions in host cells, and this oncoprotein primarily targets IκB kinase complex in the cytoplasm, resulting in persistent activation of NF-κB and upregulation of its responsive gene expressions that are crucial for T cell survival and cell cycle progression. We here review recent advances for the pathological roles of Tax in modulating IκB kinase activity. We also discuss our recent observation that Tax connects the IκB kinase complex to autophagy pathways. Understanding Tax-mediated pathogenesis will provide insights into development of new therapeutics in controlling HTLV-1-associated diseases.

Cellular Factors Involved in HTLV-1 Entry and Pathogenicit

Human T cell leukemia virus type 1 (HTLV-1) is the causative agent of adult T cell leukemia (ATL) and HTLV-1 – associated myelopathy and tropical spastic paraparesis (HAM/TSP). HTLV-1 has a preferential tropism for CD4 T cells in healthy carriers and ATL patients, while both CD4 and CD8 T cells serve as viral reservoirs in HAM/TSP patients. HTLV-1 has also been detected other cell types, including monocytes, endothelial cells, and dendritic cells. In contrast to the limited cell tropism of HTLV-1 in vivo, the HTLV receptor appears to be expressed in almost all human or animal cell lines. It remains to be examined whether this cell tropism is determined by host factors or by HTLV-1 heterogeneity. Unlike most retroviruses, cell-free virions of HTLV-1 are very poorly infectious. The lack of completely HTLV-1-resistant cells and the low infectivity of HTLV-1 have hampered research on the HTLV entry receptor. Entry of HTLV-1 into target cells is thought to involve interactions between the env (Env) glycoproteins, a surface glycoprotein (surface unit), and a transmembrane glycoprotein. Recent studies have shown that glucose transporter GLUT1, heparan sulfate proteoglycans (HSPGs), and neuropilin-1 (NRP-1) are the three proteins important for the entry of HTLV-1. Studies using adherent cell lines have shown that GLUT1 can function as a receptor for HTLV. HSPGs are required for efficient entry of HTLV-1 into primary CD4 T cells. NRP-1 is expressed in most established cell lines. Further studies have shown that these three molecules work together to promote HTLV-1 binding to cells and fusion of viral and cell membranes. The virus could first contact with HSPGs and then form complexes with NRP-1, followed by association with GLUT1. It remains to be determined whether these three molecules can explain HTLV-1 cell tropism. It also remains to be more definitively proven that these molecules are sufficient to permit HTLV-1 entry into completely HTLV-1-resistant cells.

Interaction between the HTLV-1 envelope and cellular proteins: impact on virus infection and restriction

The first human retrovirus, human T-lymphotropic virus 1 (HTLV-1), was discovered 30 years ago. Despite intensive study, the cell surface molecules involved in virus entry have only been identified over the past few years. Three molecules form the receptor complex for HTLV-1: glucose transporter 1, neuropilin 1 and heparan sulfate proteoglycans. Another molecule on the surface of dendritic cells, DC-SIGN, may play a role in dendritic cell-mediated infection of cells. In addition to the cell surface molecules used for entry, the HTLV-1 envelope interacts with cellular proteins, enabling the virus to traffic by exploiting cellular delivery pathways. To facilitate both these steps, HTLV-1 encodes motifs that mimic cellular binding partners for the trafficking system and ligands for the receptors. Here we review the interactions between the HTLV-1 envelope and cellular proteins.

Molecular determinants of human T-lymphotropic virus type 1 transmission and spread

Human T-lymphotrophic virus type-1 (HTLV-1) infects approximately 15 to 20 million people worldwide, with endemic areas in Japan, the Caribbean, and Africa. The virus is spread through contact with bodily fluids containing infected cells, most often from mother to child through breast milk or via blood transfusion. After prolonged latency periods, approximately 3 to 5% of HTLV-1 infected individuals will develop either adult T-cell leukemia/lymphoma (ATL), or other lymphocyte-mediated disorders such as HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The genome of this complex retrovirus contains typical gag, pol, and env genes, but also unique nonstructural proteins encoded from the pX region. These nonstructural genes encode the Tax and Rex regulatory proteins, as well as novel proteins essential for viral spread in vivo such as, p30, p12, p13 and the antisense encoded HBZ. While progress has been made in the understanding of viral determinants of cell transformation and host immune responses, host and viral determinants of HTLV-1 transmission and spread during the early phases of infection are unclear. Improvements in the molecular tools to test these viral determinants in cellular and animal models have provided new insights into the early events of HTLV-1 infection. This review will focus on studies that test HTLV-1 determinants in context to full length infectious clones of the virus providing insights into the mechanisms of transmission and spread of HTLV-1.

Arsenic trioxide inhibits human t cell-lymphotropic virus-1-induced syncytiums by down-regulating gp46

Adult T-cell leukemia (ATL) is a severe chemotherapy-resistant malignancy associated with prolonged infection by the human T cell-lymphotropic virus 1 (HTLV-1). One approach to prevent the onset of ATL is to inhibit the growth/transmission of HTLV-1 infected cells using arsenic trioxide (As(2)O(3)). However, there are no reports on the transmission inhibitory effect of As(2)O(3). In this study, we reveal that As(2)O(3) exerts an inhibitory effect on syncytium formation between HTLV-1 infected MT-2 and HeLa cells. In addition, Western blot analysis revealed that the HTLV-1 derived envelope protein gp46 was down regulated by As(2)O(3) treatment, suggesting that As(2)O(3) may inhibit HTLV-1 virus transmission via down-regulation of gp46. These results suggest that As(2)O(3) may be a promising drug to treat refractory HTLV-1-related diseases.

Intersubunit disulfide isomerization controls membrane fusion of human T-cell leukemia virus Env

Human T-cell leukemia virus (HTLV-1) Env carries a typical disulfide isomerization motif, C(225)XXC, in the C-terminal domain SU. Here we have tested whether this motif is used for isomerization of the intersubunit disulfide of Env and whether this rearrangement is required for membrane fusion. We introduced the C225A and C228A mutations into Env and found that the former but not the latter mutant matured into covalently linked SU-TM complexes in transfected cells. Next, we constructed a secreted Env ectodomain and showed that it underwent incubation-dependent intersubunit disulfide isomerization on target cells. However, the rearrangement was blocked by the C225A mutation, suggesting that C(225) carried the isomerization-active thiol. Still, it was possible to reduce the intersubunit disulfide of the native C225A ectodomain mutant with dithiothreitol (DTT). The importance of the CXXC-mediated disulfide isomerization for infection was studied using murine leukemia virus vectors pseudotyped with wild-type or C225A HTLV-1 Env. We found that the mutant Env blocked infection, but this could be rescued with DTT. The fusion activity was tested in a fusion-from-within assay using a coculture of rat XC target and transfected BHK-21 effector cells. We found that the mutation blocked polykaryon formation, but this could be reversed with DTT. Similar DTT-reversible inhibition of infection and fusion was observed when a membrane-impermeable alkylator was present during the infection/fusion incubation. We conclude that the fusion activity of HTLV-1 Env is controlled by an SU CXXC-mediated isomerization of the intersubunit disulfide. Thus, this extends the applicability of the isomerization model from gammaretroviruses to deltaretroviruses.

In vivo analysis of replication and immunogenicity of proviral clones of human T-lymphotropic virus type 1 with selective envelope surface-unit mutations

Human T-cell leukemia virus type 1 (HTLV-1) is the causative agent of adult T-cell lymphoma/leukemia (ATL). The HTLV-1 envelope gene exhibits limited variability when examined from infected individuals, but has not been tested using infectious clones of the virus in animal models. In vitro assays indicate that HTLV-1 envelope (Env) Ser75Ile, Asn95Asp, and Asn195Asp surface unit (SU) mutants are able to replicate in and immortalize lymphocytes. Herein, we examined the effects of these Env mutants in rabbits inoculated with HTLV-1 immortalized ACH.75, ACH.95, or ACH.195 cell lines (expressing full-length molecular clones with the SU mutations) or the ACH.1 cell line (expressing wild-type SU). All rabbits became infected, and the fidelity of the mutations was maintained throughout the 8-week study. However, SU point mutations resulted in decreased antibody responses to viral group-associated antigen (Gag) and Env antigens. ACH.195 rabbits had a selective decreased antibody response to SU, and one ACH.195 rabbit had an antibody response to both HTLV-1 and HTLV-2 SUs. Some mutant inoculation groups had altered proviral loads. However, peripheral-blood mononuclear cell (PBMC) proviral loads did not correlate with antibody responses. Our data are the first to demonstrate that mutations in critical determinants of HTLV-1 Env SU altered antibody responses and proviral loads, but do not prevent viral replication in vivo.

New approach for generation of neutralizing antibody against human T-cell leukaemia virus type-I (HTLV-I) using phage clones

We have screened a phage peptide library to address whether clones binding to a monoclonal antibody (mAb) could be isolated and if the selected phage particles would be able to elicit an in vivo immune response against the original antigen. A phage peptide library, consisting of seven random amino acids inserted in the minor coat protein (pIII), was screened for specific binding to a rat mAb LAT-27, which is capable of neutralizing human T-cell leukaemia virus type-I (HTLV-I) by binding to its envelope gp46 epitope, (amino acids LPHSNL). Total 37 clones were selected from the library and one clone named 4-2-22 was tested for its immunogenicity in three rabbits. The all rabbit immune sera showed strong binding activity to a gp46 peptide carrying the neutralization sequence, stained gp46-expressing cells and neutralized HTLV-I in vitro as determined by cell fusion inhibition assay. These results show that the selected phage clone was capable of mimicking the epitope recognized by a HTLV-I neutralizing mAb, and it can be used as an immunogen to induce protective immune response against HTLV-I. Thus, the present methodology could be one of the approaches to develop vaccines against infectious agents in a simple and inexpensive way.

HTLV-1 structural proteins

HTLV-1 structural proteins do not appear to ensure virus transmission as efficiently as most other retrovirus structural proteins do, whereas all other retroviruses can be transmitted via either free virions or cell-to-cell contacts, infection by HTLV-1 by free virions is very inefficient, and effective infection requires the presence of HTLV-1 infected cells. This characteristic feature of HTLV-1 provides a unique tool which can be used to analyse retrovirus cellular transmission in the absence of simultaneous cell-free infection. Here we summarise what is known about HTLV-1 structural proteins and identify the questions about these proteins which remain to be answered.

Characterization of envelope glycoprotein mutants for human T-cell leukemia virus type 1 infectivity and immortalization

The human T-cell leukemia virus type 1 (HTLV-1) envelope protein is required for virus spread. This study further characterizes the role of the envelope protein in HTLV-1 immortalization. Viruses with single amino acid substitutions within the SU protein at residue 75, 81, 95, 101, 105, or 195 or with a C-terminal cytoplasmic domain truncation (CT), as well as an envelope-null (EN) virus, were generated within an infectious molecular clone, ACH. Transfection of 293T cells resulted in the release of similar amounts of virus particles from all of the mutants as determined by p19 enzyme-linked immunosorbent assay and immunoblot analysis of Gag in cell lysates and supernatants. The virus particles from all mutants except ACH-101, ACH-CT, and ACH-EN were infectious for B5 macaque cells in cell-free and cell-to-cell transmission assays and were capable of immortalizing transfected CD4(+) lymphocytes. These results indicate that HTLV-1 spread is required for immortalization.

Malignancy: Human T-Cell Lymphotropic Virus Type I and Adult T-Cell Leukaemia/Lymphoma

Adult T-cell leukaemia/lymphoma (ATLL) was first identified in Japan in 1977 [1,2]. The causative agent, the human T-lymphotropic virus type I (HTLV-I), was isolated 3 years later by Gallo's group from a patient initially diagnosed as having mycosis fungoides but subsequently reclassified as a case of ATLL [3]. Since this time, much has been discovered about the molecular pathogenesis of the disease. Despite this, treatment of ATLL remains disappointing and the prognosis of acute and lymphoma types poor. In the United Kingdom, cases of ATLL are mainly restricted to people of Afro-Caribbean descent but the disease is of general importance because ATLL has also been reported in non-endemic areas and may possibly spread into other populations via blood transfusion as blood donors in the UK are currently not screened for HTLV-I.

The NH2-terminal domain of the human T-cell leukemia virus type 1 capsid protein is involved in particle formation

The human immunodeficiency virus type 1 (HIV-1) and human T-cell leukemia virus type 1 (HTLV-1) capsid proteins (CA) display similar structures formed by two independently folded N-terminal (NTD) and C-terminal (CTD) domains. To characterize the functions harbored by the HTLV-1 CA domains in particle formation, 12 sites scattered throughout the protein were mutated. The effects of the mutations on Gag membrane binding, proteolytic processing, and virus-like particle secretion were analyzed. It appears that the NTD is the major partner of indirect or direct Gag-Gag interactions. In particular, most of the NTD mutations impaired virion morphogenesis, and no mutation located in the NTD could be fully rescued by coexpression of wild-type Gag. In contrast, the CTD seems not to be involved in Gag-Gag interactions. Nevertheless, an unknown function required for particle formation is located in the CTD. Thus, despite an overall structural similarity between the HIV-1 and HTLV-1 CA proteins, their NTDs and CTDs exhibit different functions.

Myristoylation of human immunodeficiency virus type 1 gag protein is required for efficient env protein transportation to the surface of cells

Highly conserved amino acids in the N-terminal region of the human immunodeficiency virus type 1 (HIV-1) Pr55(gag) are recognized to be critical for the attachment of myristic acid. We previously reported that the env protein was not detected on the cell surface by blocking of N-myristoylation of Pr55(gag) with N-myristoyl glycinal diethylacetal. Here, we constructed a mutant by substituting the N-terminal glycine of Pr55(gag) with alanine to demonstrate that N-myristoylation of Pr55(gag) is required for efficient env protein transportation to the cell surface. The expression level of the env protein on the surface of Jurkat cells transfected with the myristoylation-defective phenotype was observed to be significantly reduced by electron microscopic analyses with a gold-labeled monoclonal antibody against the env protein. In addition, Jurkat cells transfected with the myristoylation-defective phenotype lost the ability of envelope-mediated cell-to-cell fusion. The results suggest that N-myristoylation of the HIV-1 gag protein is necessary for efficient env protein transportation to the cell surface.

Influence of Rex and intronic sequences on expression of spliced mRNAs produced by human T cell leukemia virus type I

Expression of the incompletely spliced HTLV-I mRNAs relies on the viral posttranscriptional activator Rex, whose interaction with the Rex-responsive element (RXRE) overcomes effects of cis-acting repressive sequences (CRSs). Studies based on heterologous reporter plasmids identified an intronic CRS in the 5' LTR and a CRS that overlaps with the RXRE. The present study investigated the effects of these elements in the context of spliced viral mRNAs encoding p21Rex (mRNA 1-3), Tax/Rex (mRNA 1-2-3), and Tof (mRNA 1-2-B). All three mRNAs were inefficiently expressed when transcribed in their mature intronless form, with the p21Rex mRNA showing the weakest expression. In contrast, efficient expression of p21Rex was obtained from a plasmid containing the 5' LTR and 3' portion of the genome that encoded a spliceable RNA. The defective expression of the intronless mRNAs reflected the inhibitory activity of the RXRE and the lack of 5' intronic sequences. Insertion of an intronic 5' LTR segment located upstream of the 5' CRS overcame Rex dependence conferred by the RXRE. The activity of this segment was mapped to the major splice donor and sequences overlapping with, but functionally distinct from, a previously described transcriptional enhancer. The three mRNAs responded differently to Rex and to insertion of the constitutive transport element of simian retrovirus type 1. Taken together, these results suggest that expression of the spliced mRNAs is controlled by the relative influence of positive and negative sequences present on the primary transcript as well as the Rex-RXRE interaction.

Two types of HTLV-1 particles are released from MT-2 cells

The MT-2 cell line transformed by human T-cell leukemia virus type 1 (HTLV-1) contains one complete provirus and seven defective proviruses. Four defective genomes have an identical structure (LTR-MA-deltaCA-pX-LTR) with an open reading frame that spans from MA to pX, giving rise to a 3.4-kb (24S) RNA transcript encoding a chimeric Gag-pX protein, p28. MT-2 cells release two distinct types of virions. The major "classic" type of particle has a buoyant density of 1.155-1.16 g/cm3 and contains the standard HTLV-I structural proteins and reverse transcriptase (RT). In addition, about 5% of particles are "light," approximately 1.12 g/cm3, and contain p28, RT activity, and the 3.4-kb RNA transcript. RT-PCR and in vitro translation indicate that some of the classic HTLV-1 particles package 3.4-kb RNA as well as full-length 8.5-kb RNA. In addition to matrix features, the p28 protein has a motif resembling a zinc finger at the C-terminal, pX0 region, which may play a role in the assembly of the defective light virions.

The origin and evolution of human T-cell lymphotropic virus types I and II

Studies on human T-cell lymphotropic virus types I (HTLV-I) and II (HTLV-II) are briefly reviewed from the viewpoint of molecular evolution, with special reference to the evolutionary rate and evolutionary relationships among these viruses. In particular, it appears that, in contrast to the low level of variability of HTLV-I among different isolates, individual isolates form quasispecies structures. Elucidating the mechanisms connecting these two phenomena will be one of the future problems in the study of the molecular evolution of HTLV-I and HTLV-II.

Induction of antibody responses that neutralize human T-cell leukemia virus type I infection in vitro and in vivo by peptide immunization

In order to define neutralization regions on the envelope antigen of human T-cell leukemia virus type I (HTLV-I), we have generated a number of new anti-envelope gp46 monoclonal antibodies from rats and mice. Epitopes recognized by new monoclonal antibodies which could neutralize HTLV-I in syncytium and transformation inhibition assays were localized to sequences in gp46 from amino acids 186 to 193, 190 to 195, 191 to 195, 191 to 196, and 194 to 199. Ovalbumin-conjugated synthetic gp46 peptides containing these neutralization epitopes, pep190-199 (a synthetic gp46 peptide containing amino acids 190 to 199) and pep180-204, but not pep185-194 or pep194-203, could give rise to HTLV-I-neutralizing antibody responses in rabbits. These immune or nonimmune rabbits were then challenged with HTLV-I by intravenous inoculation with 5 x 10(7) live HTLV-I-producing ILT-8M2 cells. By a PCR assay, it was revealed that HTLV-I provirus was detected in peripheral blood lymphocytes from nonimmune and pep288-312-immunized rabbits, whereas the provirus was not detected in peripheral blood lymphocytes from pep190-199- and pep180-204-immunized rabbits over an extended period. These results suggest that the induction of anti-gp46 neutralizing antibody responses by immunization with synthetic peptides has the potential to protect animals against HTLV-I infection in vivo.

Identification of functional regions in the human T-cell leukemia virus type I SU glycoprotein

Single conservative and nonconservative amino acid substitutions were introduced into the gp45 external envelope protein (SU) of human T-cell leukemia virus type I (HTLV-I). The mutated amino acids were those identified as being conserved in HTLV-I, HTLV-II, and simian T-cell leukemia virus type I (but not in bovine leukemia virus). The mutated envelopes were tested for intracellular maturation and for function. Mutants with three major phenotypes could be defined: (i) 9 mutants with a wild-type phenotype, which included most of the conservative amino acid changes (five of seven) distributed throughout the SU protein; (ii) 8 mutants with affected intracellular maturation, 6 of which define a region in the central part of the SU protein essential for correct folding of the protein; and (iii) 13 mutants with normal intracellular maturation but impaired syncytium formation. These mutations likely affect the receptor binding step or postbinding events required for fusion. Five of these mutations are located between amino acids 75 and 101 of the SU protein, in the amino-terminal third of the molecule. The other mutations involve positions 170, 181, 195, 197, 208, 233, and 286, suggesting that two other domains, one central and one carboxy terminal, are involved in HTLV-I envelope functions.

Mechanism of inhibitory effect of dextran sulfate and heparin on human T-cell lymphotropic virus type I (HTLV-I)-induced syncytium formation in vitro: role of cell-to-cell contact

Cell-to-cell contact is usually essential for syncytium formation by HTLV-I-infected cell lines. The present study was undertaken to determine the inhibitory effect of polyanionic compounds, dextran sulfate and heparin, on HTLV-I-induced syncytium formation, as demonstrated by the fusion of HTLV-I-infected cells with target cells. These two compounds almost completely blocked syncytium formation in the early phase of the reaction at a concentration of 125 micrograms/ml, but dextran, as a control, did not inhibit it at concentrations up to 625 micrograms/ml. 50% inhibition of syncytium formation was detected at a concentration of 2 micrograms/ml of dextran sulfate 5000, 3 micrograms/ml of dextran sulfate 8000 and 8 micrograms/ml of heparin. The binding of radiolabeled HTLV-I-infected cells (HCT-1) to the target cells was inhibited by addition of dextran sulfate and heparin, and the inhibitory effects were concentration-dependent. No marked changes were detected in the expression of adhesion molecules on the virus-infected cells and target cells, and in the expression of envelope proteins on the virus-infected cells after exposing them to the polyanionic compounds. These results suggest that the blocking of cell-to-cell contact by polyanionic compounds, probably independent of surface adhesion molecules, is important for their inhibitory effect on HTLV-I-induced syncytium formation.

HTLV-I, HIV-I, and hepatitis B and C viruses in Western Province, Papua New Guinea: a serological survey

Seven hundred and twenty-three serum samples from individuals in 13 Gidra-speaking villages in Western Province, Papua New Guinea were tested for evidence of infection with human T-lymphotropic virus type I (HTLV-I), human immunodeficiency virus type I (HIV-I), hepatitis B virus (HBV) and hepatitis C virus (HCV). No samples were positive for antibodies to HIV-I. Antibodies to HTLV-I were found in 13 samples (1.8%), HBV surface antigens (HBsAg) were found in 86 samples (11.9%), and antibodies to HCV were found in 30 samples (4.1%). Six (46.2%) of 13 HTLV-I positive samples were positive for HCV or HBsAg. The seropositive rate varied in different villages and the incidence of HTLV-I and HCV was higher in coastal and riverine areas than inland.

Indications for the presence of antibodies cross-reactive with HTLV-I/II, but not HIV, in patients with myelodysplastic syndrome

Serological evidence is presented for the fact that patients with the myelodysplastic syndrome exhibit a statistically significant reactivity in confirmatory assays for antibodies to human T-lymphotropic viruses types I and II (HTLV-I/II). This antibody reactivity, evident by indirect immunofluorescence and Western blot, was not confined to HTLV core antigens but extended to native and recombinant envelope glycoproteins. The effect was also observed in cases of acute myeloic leukemia, albeit to a lesser degree. It was essentially absent from patients with chronic myeloic leukemia or lymphocytic leukemias and healthy or multitransfused controls. No antibodies to human immunodeficiency viruses types 1 or 2 were detected in any of the specimens. The investigated clinical population had no known risk factor for retroviral infection other than a history of multiple platelet transfusions, and none of the specimens was seropositive for HTLV-I or HTLV-II according to recommended criteria. The cause of this cross-reactivity remains to be determined.

T-cell lymphoma in Singapore: pathology, clinical findings and association with HTLV-1 antibodies

Of 128 cases of malignant lymphomas studied in Singapore between 1986 and 1988, 28 were identified as peripheral T-cell lymphomas. Sera from two of the 128 cases were positive for HTLV-1 antibodies and both cases had the clinical and pathological features of adult T-cell leukaemia/lymphoma. The pathological and clinical features of the 28 cases of peripheral T-cell lymphoma are presented in detail. Survival data indicated no significant difference between the low grade and high grade histological types. Three of the patients had previous or concomitant malignancies. The percentage of T-cell lymphomas associated with HTLV-1 infection in Singapore is low compared to those areas in which HTLV-1 is endemic.

Human T-cell leukemia virus type I envelope protein maturation process: requirements for syncytium formation

The human T-cell leukemia virus type I (HTLV-I) envelope protein is synthesized as a gp61 precursor product cleaved into two mature proteins, a gp45 exterior protein and a gp20 anchoring the envelope at the cell membrane. Using N-glycosylation inhibitors and site-directed mutagenesis of the potential glycosylation sites, we have studied the HTLV-I envelope intracellular maturation requirements for syncytium formation. We show here that experimental conditions resulting in the absence of precursor cleavage (tunicamycin, monensin treatments, and use of inhibitors of the reticulum steps of the N glycosylations) also result in no cell surface expression of envelope protein. The lack of syncytium formation observed in these cases is thus explained by incorrect intracellular transport. When the precursor is cleaved in the Golgi stack (no treatment or treatment with inhibitors of the Golgi steps of the N glycosylations), it is transported to the cell surface in all the cases examined. Syncytium formation is markedly reduced, however, when Golgi glycosylations are incorrect, which shows that the sugar moieties are involved in the envelope functions. Site-directed mutagenesis demonstrates that each of the five potential glycosylation sites is actually glycosylated. Glycosylation of sites 1 and 5 is required for normal maturation, whereas that of sites 2, 3, and 4 is dispensable. Glycosylation of each site, however, is required for normal syncytium formation. Altogether, the restraints exerted by the cell for the HTLV-I envelope to be transported and functional are very high, which might play a role in the observed conservation of the envelope amino acid sequence between various strains.

Enhancement of human immunodeficiency virus type 1 infection by antisera to peptides from the envelope glycoproteins gp120/gp41

Human immunodeficiency virus type 1 (HIV-1) envelope glycoproteins (gp120 and gp41) elicit virus-neutralizing antibodies (VNAB) and also antibodies enhancing HIV-1 infection (EAB). Several epitopes eliciting VNAB have been defined, the principal virus-neutralizing determinant being assigned to the V3 loop of gp120. To provide a background for a rational design of anti-HIV vaccines, it also appears important to define domains eliciting EAB. This was accomplished by screening antisera against synthetic peptides covering almost the entire sequence of gp120/gp41 for their enhancing effects on HIV-1 infection of MT-2 cells, a continuous T cell line. Many (16/30) of the antisera significantly enhanced HIV-1 in the presence of human complement. Antibodies to complement receptor type 2 (CR2) abrogated the antibody-mediated enhancement of HIV-1 infection. Antisera to V3 hypervariable loops of 21 distinct HIV-1 isolates were also tested for their enhancing effects on HIV-1IIIB infection. 11 of these sera contained VNAB and 10 enhanced HIV-1IIIB infection. All antisera with virus-enhancing activity contained antibodies crossreactive with the V3 loop of HIV-1IIIB, and the virus-enhancing activity increased with increasing serological crossreactivity. These results suggest that immunization with antigens encompassing V3 loops may elicit EAB rather than protective antibodies if epitopes on the immunogen and the predominant HIV-1 isolate infecting a population are insufficiently matched, i.e., crossreactive serologically but not at the level of virus neutralization.

Purification and characterization of human T-cell leukemia virus type I protease produced in Escherichia coli

Human T-cell leukemia virus type I (HTLV-I) protease has been purified to homogeneity from a strain of recombinant Escherichia coli. The protease was expressed as a larger precursor, which was autoprocessed to form a mature protease. Protein chemical analyses revealed the coding sequence of mature protease, which agreed with the putative sequence predicted from the sequence of bovine leukemia virus protease. The purified protease processed the natural substrate gag precursor (p53) to form gag p19 and gag p24. The protease activity was inhibited by pepstatin A. These results provide direct evidence that this protease belongs to the aspartic protease family and has an activity consistent with the protease in HTLV-I virion.

Human cellular src gene product: identification of the myristoylated pp60c-src and blockage of its myristoyl acylation with N-fatty acyl compounds resulted in the suppression of colony formation

A p60K protein in human colon adenocarcinoma tumor cell lines was identified as a myristoylated pp60c-src by fluorography and radioimmunoprecipitation analysis. Prevention of the myristoylation of pp60c-src was determined with N-fatty acyl glycinal compounds. Of the compounds tested, N-myristoyl glycinal diethylacetal, N-lauroyl glycinal diethylacetal, N-myristoyl glycyl glycinal diethylacetal, and N-myristoyl-4-aminobutyl-aldehyde diethylacetal strongly blocked the myristoylation, but N-decanoyl glycinal diethylacetal and N-palmitoyl glycinal diethylacetal did not. The myristoyl blocking compounds depressed colony formation, cell proliferation, and specific localization to the plasma membrane of pp60c-src. The results taken together suggest that myristoylation of the c-src oncogene product may be very important for tumorigenicity of c-src gene expressed cells.

Development and evaluation of a human T-cell leukemia virus type I serologic confirmatory assay incorporating a recombinant envelope polypeptide

A recombinant protein derived from the gp21 region of the human T-cell leukemia virus type I (HTLV-I) env gene was synthesized in Escherichia coli and purified by reversed-phase high-performance liquid chromatography. The purified protein was free of contaminating bacterial proteins and retained reactivity with human HTLV-I- and HTLV-II-positive sera and a gp21 monoclonal antibody. An immunoblot procedure using the recombinant polypeptide in conjunction with native viral proteins was more sensitive than the conventional immunoblot and radioimmunoprecipitation confirmatory assays for detection of antibodies to HTLV-I and HTLV-II env-encoded gene products. The recombinant protein was equally reactive with sera from polymerase chain reaction-confirmed HTLV-I or HTLV-II infections. Furthermore, on the basis of the differential reactivities of gp21-positive sera with the HTLV-I p19 and p24 gag-encoded proteins, an algorithm was proposed to distinguish exposure to HTLV-I from exposure to HTLV-II. These results establish the utility of a modified immunoblot assay incorporating a recombinant envelope polypeptide as an alternative to existing HTLV-I-confirmatory assays.

Expression of HTLV-I envelope protein fused to hydrophobic amino-terminal peptide of baculovirus polyhedrin in insect cells and its application for serological assays

The envelope of human T-cell leukemia virus type I (HTLV-I) consists of two glycoproteins gp46 and p20E. Recombinant envelope proteins were produced by using an expression vector derived from insect baculovirus, Bombyx mori nuclear polyhedrosis virus. Polyhedrin fusion proteins C182, N147, and N287 contained whole region p20E, C-terminal half of gp46, and almost whole region gp46, respectively. N147 and N287 were suggested to be processed forms resulting from internal cleavage by cellular enzymes. In cultured cells and the insect larvae, C182 and N147 were produced abundantly enough to be purified to homogeneity; however, N287 was produced poorly and not purified. The purified proteins were recognized by HTLV-I-infected human sera and shown to be highly specific antigens for blood screening systems.

Generation and characterization of monoclonal antibodies against multiple epitopes on the C-terminal half of envelope gp46 of human T-cell leukemia virus type-I (HTLV-I)

In order to study the antigenicity of envelope 46 kDa glycoprotein (gp46) of human T-cell leukemia virus type-I (HTLV-1), we have generated monoclonal anti-gp46 antibodies (MAbs), REY-7, REY-11, REY-16, REY-30, MET-2 and MET-3 from rats and mice. Immunoblot and immunofluorescence assays showed that these MAbs recognize gp46 and its related antigens, and specifically stained HTLV-I-bearing cells. All MAbs reacted with a recombinant gp46 antigen, N147, expressing the 147 amino acids in the C-terminal half of gp46. By using various synthetic peptides corresponding to the gp46 sequence, epitopes recognized by REY-7 and MET-3, REY-11 and REY-16, and REY-30 were mapped to regions corresponding to the amino acids 175-199, 253-282 and 288-312, respectively. MET-2 did not react with any of the peptides used. These results indicate that the present MABs are directed against at least 4 distinct epitopes expressed on the C-terminal half of gp46. The binding of these MAbs to gp46 was specifically inhibited by sera from HTLV-I-infected individuals, but none of these MAbs inhibited the cell fusion activity of HTLV-I.

HTLV-I antibody studies in villagers in East Sepik Province, Papua New Guinea

Serum samples collected in 1984 during a malariometric survey of two villages in the East Sepik Province of Papua New Guinea were tested for antibodies to HTLV-I. None of the villagers showed any symptoms suggestive of retrovirus infection. Eighteen of the 186 (9.5%) sera tested at that time were found to be positive. Blood samples were subsequently obtained from fifteen of the eighteen positives and subjected to analysis by enzyme-linked immunosorbent assay (ELISA), radioimmuno assay (RIA), radioimmunoprecipitation assay (RIPA), and Western blot (WB). Fourteen of the fifteen gave a positive ELISA response, but none were unequivocally positive by p 24 RIA. All sera tested were reactive to gag antigens by WB, but gave "indeterminate" results currently accepted criteria. Notably absent from the WB profiles of all of the study subjects was an antibody response to HTLV-I envelope protein gp 46. It is possible that these antibody responses are directed against a variant of HTLV-I or to a novel retrovirus which possesses core antigens similar to those of HTLV-I but has different envelope antigens. Until a virus is isolated, or the viral genome is identified in infected lymphocytes, the possibility remains that the response may be due to factors unrelated to retrovirus infection.

Intracellular processing and immunogenicity of the envelope proteins of human T-cell leukemia virus type I that are expressed from recombinant vaccinia viruses

Two types of recombinant vaccinia viruses (VVs) expressing the env gene of the human T-cell leukemia virus type I (HTLV-I) were reported previously. One recombinant VV, WR-proenv1, synthesized the authentic env protein. In the other recombinant VV, WR-env17, the env gene was inserted within the signal sequence of the VV hemagglutinin (HA) gene, so that the reading frame for the env gene was in phase with that for the HA gene. Comparative studies were performed on the mode of expression and processing of the env proteins in relation to their immunogenicity. In WR-env17-infected cells, translation was initiated exclusively from the initiation methionine of the HA to produce nascently the chimeric env protein, including the altered HA signal peptide. Both this altered HA signal peptide and the internalized env signal peptide functioned as insertion signals for the endoplasmic reticulum. Although about half of the nascent chimeric protein was cleaved at the carboxyl terminus of the internalized env signal peptide to produce the authentic env protein, the other half was cleaved at the carboxyl terminus of the altered HA signal peptide alone to synthesize the chimeric protein. These events led to a less efficient transport of the env protein produced by WR-env17 from the rough endoplasmic reticulum to the Golgi apparatus than that of the authentic env protein synthesized by WR-proenv1. The efficiency of the processing and transport of the env protein affected the immunogenicity of these two recombinant VVs.

Antimyristoylation of the gag proteins in the human immunodeficiency virus-infected cells with N-myristoyl glycinal diethylacetal resulted in inhibition of virus production

The gag proteins of human retroviruses such as human immunodeficiency virus (HIV-1) are specifically myristoylated in their amino termini (1, 2, 3). N-myristoyl glycinal diethylacetal (N-Myr-GOA) and other N-Myr-compounds (N-Myr-Gly-GOA, N-Myr-Gly-Gly-GOA and N-Myr-Gly-Gly-Gly-GOA) were newly synthesized and investigated for activity of antimyristoylation of these gag proteins and for influence on viral replication. Of the N-Myr-compounds tested, N-Myr-GOA most severely inhibited the protein myristoylation; N-Myr-Gly-GOA also inhibited it, but moderately. Furthermore, it was observed that N-Myr-GOA at 20 microM caused noticeable inhibition (about 80%) of the production of mature HIV in the HIV-1-infected MT-4 cells. In this system, N-Myr-GOA substantially inhibited more than 90% of the N-myristoylation of p17 gag protein produced in the HIV-1-infected MT-4 cells. These results suggest that the N-myristoylation of p17 gag protein of HIV-1 may be essential in its structural assembly or maturation.

A novel antibody against a synthetic NH2-terminal myristoyl glycyl src peptide can detect pp60v-src, the transforming protein of Rous sarcoma virus

Novel antibodies were raised against a synthetic NH2-terminal myristoyl(Myr-) tetrapeptide(N-Myr-Gly-Ser-Ser-Lys) which is characteristic of an NH2-terminal portion of pp60v-src, the transforming protein of Rous sarcoma virus. Antisera raised against N-Myr-Gly-Ser-Ser-Lys-haemocyanin reacted with 125I-albumin conjugates with N-Myr-Gly-Ser-Ser-Lys. The immunoreaction was competed for by haemocyanin as well as albumin conjugated with this N-Myr-peptide, while underivatized proteins or an NH2-terminal octapeptide (Gly-Ser-Ser-Lys-Ser-Lys-Pro-Lys) had no effect. N-Myr-Gly-Ser-Ser-Lys-(125I)tyramine was also recognized by the antibody. The reaction was competed for by N-Myr-Gly-Ser-Ser-Lys, but not by Gly-Ser-Ser-Lys-Ser-Lys-Pro-Lys. These results suggest a high affinity of the antibody for an N-Myr-peptide moiety. The major (3H)myristate-labelled protein of an apparent molecular weight of 60,000 was detected from chick embryo fibroblasts transformed by Rous sarcoma virus (tsNY68). This protein was demonstrated to possess N-Myr-Gly-Ser-Ser-Lys by the immunoprecipitation and HPLC analyses. Furthermore, the entire circumference of the transformed cells was stained by the antibody upon an immunofluorescent microscopic observation. Thus, these results taken together indicate that the haptenic antibody raised against the myristoyl peptide is useful to detect pp60v-src protein.

Antibodies to an NH2-terminal myristoyl glycine moiety can detect NH2-terminal myristoylated proteins in the retrovirus-infected cells

Novel antibodies were raised against a synthetic NH2-terminal myristoyl glycine moiety which is characteristic of N-myristoyl-proteins. Antisera raised against N-myristoyl-Gly-hemocyanin reacted with N-myristoyl-Gly-[125I]albumin. The immunoreaction was competed for by albumin conjugated with N-myristoyl-glycine, while underivatized albumin had no effect. Of the [3H]myristate-labeled proteins detected, pp60v-src, which is a transforming protein of Rous sarcoma virus, and p19gag and p17gag, which are core proteins in the human T-cell leukemia virus and the human immunodeficiency virus, were identified as N-myristoylated proteins by the radioimmunoprecipitation analyses with the antibody.

Detection of high concentrations of HTLV-1 p24 and a novel gag precursor, p45, in serum immune complexes of a healthy seropositive individual

Circulating immune complexes from sera of 6 patients with adult T-cell leukemia and 8 asymptomatic carriers infected with the human T-cell leukemia virus type 1 (HTLV-1) were precipitated with polyethylene glycol, and the precipitates were tested for the presence of viral antigen p24 by Western blot, using affinity-purified radiolabelled goat antibody to p24 as a probe. p24 and a larger protein of Mr 45,000 immunologically related to p24 were detected at concentrations of up to 100-200 ng/ml in one of the carriers, while all other samples were negative. The concentration of the Mr 45,000 protein in the immune complexes was considerably higher than that of p24. Analysis of an HTLV-1 producer cell line, G-11/MJ, by competition Western blots and gag-specific antibodies, showed the presence of a hitherto unrecognized viral protein p45 which contains both p19 and p24 and probably represents an intermediate precursor of these proteins. The results present direct evidence of production of HTLV-1 proteins in an asymptomatically infected individual.

Identification of HTLV-I gag protease and its sequential processing of the gag gene product

The full-length provirus of human T-cell leukemia virus type I (HTLV-I) was isolated from MT-2, a lymphoid cell line producing HTLV-I. In transfected cells, structural proteins of HTLV-I, the gag and env products, were formed and processed in the same manner as observed in MT-2 cells. The nucleotide sequence was determined for a region between the gag and pol genes of the proviral DNA clone containing an open-reading frame. The deduced amino acid sequences show that this open-reading frame encodes a putative HTLV-I protease. The protease gene (pro) of HTLV-I was investigated using a vaccinia virus expression vector. Processing of 53k gag precursor polyprotein into mature p19, p24, and p15 gag structural proteins was detectable with a recombinant plasmid harboring the entire gag- and protease-coding sequence. We demonstrated that the protease processed the gag precursor polyprotein in a trans-action. A change in the sequence Asp(64)-Thr-Gly, the catalytic core sequence among aspartyl proteases, to Gly-Thr-Gly was shown to abolish correct processing, suggesting that HTLV-I protease may belong to the aspartyl protease group. The 76k gag-pro precursor polyprotein was identified, implying that a cis-acting function of HTLV-I protease may be necessary to trigger the initial cleavage event for its own release from a precursor protein, followed by the release of p53 gag precursor protein. The p53 gag precursor protein is then processed by the trans-action of the released protease to form p19, p24, and p15.

Translation of gag, pro, and pol gene products of human T-cell leukemia virus type 2

Sequence analysis of human T-cell leukemia proviral DNA revealed three open reading frames arranged at a -1 position relative to one another. On the basis of homology to other retroviruses, these open reading frames were assigned to the gag, pro, and pol genes. To characterize the primary protein products of these genes and their modes of synthesis, a DNA clone of human T-cell leukemia virus type 2 was transcribed and translated in vitro. Analysis of the viral proteins revealed three polyproteins with molecular masses of 58, 75, and 112 kilodaltons at relative frequencies of 100:13:0.9, respectively. These proteins were mapped on the viral genome by both internal deletions and 3'-end truncations at gag, pro, and pol, respectively. The results indicate that translation of the pol gene requires two independent frameshift events, and the readthrough frequencies at the two frameshift sites appeared to be similar.

HTLV-1 in Switzerland: low prevalence of specific antibodies in HIV risk groups, high prevalence of cross-reactive antibodies in normal blood donors

Sera from various Swiss population groups were tested for antibodies against the human T-cell leukemia virus type I (HTLV-I). Particle agglutination and ELISA were performed for screening; Western blot was done for confirmation. True-positive sera were found at a prevalence of 0.12% in a cohort of 846 individuals at risk for AIDS tested in 1984-1985. Prevalences of 0.35% were found among 575 HIV-I positives tested in 1987, and of 1.3% among 292 HIV-I positives of a different group tested in 1988. The 6 positives found in our study represent the first cases of HTLV-I infection, or HIV-I/HTLV-I double infection, diagnosed in Switzerland. In addition, high proportions of sera, regardless of whether they were from normal blood donors, HIV-positives, or individuals at risk for AIDS, had antibodies that reacted weakly with one or several proteins of the size of viral gag proteins. The prevalence of such antibodies in normal donors was in the range of 10 to 40%, depending on the strictness of interpretation. Competition Western blots performed with some of these sera showed that these antibodies reacted with HTLV-I, but not with HIV-I or cellular antigens, and had a lower affinity to HTLV-I proteins than the antibodies of human or goat antisera. The results indicate that these antibodies may be induced by agents immunologically related to, but different from, HTLV-I, which are highly prevalent in the Swiss population. Oligopeptide stretches with sequence homology to HTLV-I are known to exist in various normal body proteins, several infectious agents including common viruses and protozoa, but the results might also indicate the existence of additional human retroviruses. Screening of blood donors with sensitive tests for antibodies to HTLV-I might produce an unacceptably high rate of false-positive results, if stringent rules of interpretation analogous to those common in HIV screening are not used.

Effects and virulences of recombinant vaccinia viruses derived from attenuated strains that express the human T-cell leukemia virus type I envelope gene

We constructed recombinant vaccinia viruses (RVVs) that expressed human T-cell leukemia virus type I (HTLV-I) envelope glycoproteins by using attenuated vaccinia viruses (VVs) which have much lower neurovirulence than the WR strain that is extensively used as a vector. The RVV produced from the LC16mO strain, one of the attenuated VVs, elicited a high titer of anti-HTLV-I antibody in rabbits and protected them against HTLV-I infection. The env gene was inserted into the VV hemagglutinin gene. The resultant inactivation of the hemagglutinin gene led to the attenuation of VVs, but the extent of their attenuation depended on the VV strain. The propagation of LC16mO and its RVV in rabbit brain was poorer than that of LO-1, a cloned derivative of Lister strain, and its RVV, although LC16mO replicated in other organs better than did LO-1. Taken together, these results suggest that LC16mO is a good candidate as a vector for vaccination of humans.

HTLV-1 infection in tropical spastic paraparesis: lymphocyte culture and serologic response

All 17 patients with tropical spastic paraparesis (TSP) in a series seen in the United Kingdom have antibodies to the human T cell leukemia virus type 1 (HTLV-1). Cultured peripheral blood lymphocytes from these patients formed multinucleated giant cells and reacted with sera and monoclonal antibodies to HTLV-1 in a manner identical to adult T cell leukemia-lymphoma (ATLL) patient lymphocytes. Western blot analysis failed to reveal any marked difference in the antigens recognized by sera from TSP and ATLL patients. The sera from TSP patients, their asymptomatic relatives and ATLL patients were titrated using the following assays: enzyme-linked immunosorbent assays (ELISA), particle agglutination, antibody-dependent cell-mediated cytotoxicity, and pseudotype neutralization. There were significantly stronger serologic responses in the TSP patients than in their relatives or ATLL patients. High antibody titers in the presence of replicating virus often reflect the antigen load; however, these data are also consistent with the suggestion that neurologic damage in TSP may be immunologically mediated.